As VDH-SOFT said, SparkIV or OpenIV. You can export sounds from the sound archives and port it over to the base game. Just make sure its not overwriting any other sounds. You can also port over animations. For single player playing, I ported TLaD auto-pistol animation to the DEAGLE on main GTAIV and upped the clip size to 30 arounds. You can empty a clip in about 2 seconds. lol